A certain market has both an express checkout line and a super-express checkout line. Let X, denote the number of customers in line at the express checkout at a particular time of day, and let X2 denote the number of customers in line at the superexpress checkout at the same time. Suppose the joint pmf of X] and X2 is as given in the accompanying table. X 2 0 2 3 0.08 0.08 D.04 0.00 0.08 0.1 0.05 0.06 X 1 0.05 0.04 AWNI .10 0.06 0.00 0.03 0.04 0.07 0.00 0.01 0.05 0.06 The difference between the number of customers in line at the express checkout and the number in line at the superexpress checkout is X, - X2. Calculate the expected difference. 45 X